Structural Design And Modification Of Resin-based Porous Carbon And Its Study In Lithium-sulfur Batteries

The evolution of electric vehicles,smart grids,and portable mobile devices requires batteries with higher energy density and higher power.Lithium-sulfur batteries have a high specific energy of 2600 Wh/kg,which is about 5-7 times as much as that of lithium-ion batteries.Moreover,the low price and environmental friendliness of sulfur make the lithium-sulfur batteries expected to achieve commercial mass production.Therefore,lithium-sulfur batteries have become the focus of attention of researchers in the field of new energy.However,the practical application of lithiumsulfur batteries is limited by the poor electrical conductivity of cathode materials,large volume change and shuttle effect.In this paper,porous carbon materials have been proved to effectively improve the electrochemical performance of lithium-sulfur batteries.in order to understand the influence of porous structure and atoms doped of carbon materials on the electrochemical performance of lithium-sulfur batteries,the study about porous and surface of resin-derived carbon materials was designed.Specific research contents and results are as follows:(1)The rich microporous carbon material(MPC)was synthesized by the template method and sol-gel method.Compared to carbon materials prepared without using the template method,MPC with richer microporous and mesoporous,Microporous adsorption capacity is stronger,mesoporous carbon materials than macroporous carbon materials have sufficient contact area with the electrolyte for rapid electrolyte permeation and ion transport.After carbon porous of MPC is adjusted,MPC/S-0.05 shows a high discharge capacity 1208 m Ah/g at the first cycle,and the specific capacity is maintained at 487.2 m Ah/g after 200 cycles at 0.5C.(2)The adsorption of polysulfide by MPC material is limited to physical adsorption.Especially,the introduction of N atomic can greatly strengthen the adsorption effect with lithium polysulfides through chemical bonding,so the electrochemistry performance of the Li-S battery is improving.Using urea as the nitrogen source,urea was added into the mixture solution of resorcine and formaldehyde to prepare N-doped carbon microspheres(NCS)by template method.This part is the study about the electrochemical performance of NCS for lithium-sulfur batteries.the carbon pore structure and atoms doping amount were changed by changing the pyrolysis temperature.in the range of 600-900 ?,the crystallinity of carbon decreases with the increase of temperature,the number of carbon defects increases,and the micropores and mesopores of the material become more abundant.AC impedance test shows that the electrochemical charge transfer impedance decreases with the increase of pyrolysis temperature,which indicates that the carbon defect sites increase and the porosity is more abundant,which is more conducive to the redox reaction of lithium-sulfur batteries.The specific discharge capacity of NCS/S-800 is554 m Ah/g after 50 cycles at 0.2C.(3)The specific surface area and porosity of NCS materials are low,so it is limited to payload the active substances.Turning the carbon spheres into hollow carbon spheres will provide more room to load sulfur.Therefore,the N and O co-doped hollow carbon sphere(NOHCS)was prepared by using the self-assembled template method.CV test proved that the electrode polarization of the prepared NOHCS/S-0.12 material was small and the electrochemical reversibility was strong.The first discharge specific capacity of NOHCS/S-0.12 material at 0.1C is 1029 m Ah/g,and the specific capacity of 80 cycles is maintained at 552 m Ah/g.This is attributed to the fact that the NOHCS material not only provides enough space to alleviate the volume change of the active substance and avoid the capacity attenuation caused by the pulverization and falling off of the positive electrode active substance due to repeated volume change,but also the hollow structure can bind polysulfide inside the carbon sphere and reduce the failure of the active substance caused by shuttle effect.N and O co-doping can provide multiple active sites,and use extra lone pair electrons to fix the polysulfide,which further inhibits the shuttle effect and makes the cycle performance of the battery more stable.